1. Field of the Invention
This invention relates generally to the field of fishways, and more specifically, relates to a labyrinth weir and pool fishway for passing fish upstream around an obstacle.
2. Related Art
When a manmade obstacle such as a dam is placed in a flowing body such as a river or stream, the obstacle can have a devastating impact on some species of fish within the body of water. Some types of fish such as salmon and shad need to move upstream during parts of their lives for purposes such as spawning and feeding. When an obstacle is placed in the way of these fish, upstream movement of the fish is stopped. This restriction of movement can result in the elimination of entire species of fish from that body of water.
The passage of fish around obstacles to feeding and spawning areas, upstream is an ongoing concern to many federal agencies such as the Fish and Wildlife Service (FWS) and the Environmental Protection Agency (EPA). In addition, it is a matter of concern to, among others, state and local conservation departments and agencies, non-governmental groups, utility companies, and the public. Most prominent is the need for an efficient fish passage means over dams without the need for extensive reconstruction of the dam structure or of the surrounding area.
Fishways have been designed for assisting species such as salmon to move upstream despite manmade obstacles. To be successful, the hydraulic conditions of a given fishway must be such as to not overtax the energy of the type or types of fish using the fishway. Water flow should be sufficient for fish migration, but the energy of the flow should be low enough so that the fish can travel upstream through the fishway.
A typical fishway within the prior art of the pool and weir type is illustrated in FIG. 1. The fishway 6 is comprised of a pair of fishway sides, denoted 7a and 7b, and a series of barriers, or weirs, denoted 8a, 8b, and 8c , between the sides 7a , 7b. Each pair of weirs defines a pool area therebetween. The large arrow within the fishway, denoted xe2x80x9cAxe2x80x9d, indicates the direction of water flow. A strong fish, such as a salmon moves past the weirs 8a, 8b, 8c and the pool areas defined by the weirs, and continues along the fishway in such fashion until the barrier in the waterway has been circumvented.
Existing fishways such as the prior art fishway of FIG. 1 are typically designed for fish with strong swimming and jumping capabilities such as salmon. Salmon are strong swimmers and are able to jump over moderately heights when necessary to move upstream in a river or fishway.
However, the need to preserve an entire ecosystem, and all the species within the ecosystem, has been recognized. Non-salmon and non-salmon-related fish populations have also suffered as a result of manmade obstacles in rivers. Many riverine fish are in danger because some species have a need to migrate up and down river throughout periods of their lives as well. Fishways are required, therefore, which allow all fish in a waterway to pass, rather than only the superior swimming and jumping fish. By way of example, American Shad are adversely affected by blocked upstream passage, but do not perform as well as salmon in fishways.
In accordance with the invention, a labyrinth weir and pool fishway is provided for facilitating upstream fish movement around obstacles, the fishway comprising: a pair of spaced fishway walls, and a plurality of weirs located between the fishway walls for dissipating flow energy of water flowing through the fishway, the weirs being disposed in longitudinally spaced relation along the fishway and each consecutive pair of weirs defining a pool therebetween; each of the weirs comprising: a center wall; first and second middle walls attached to the center wall on opposite sides thereof so that the first and second middle walls form an acute angle facing away from the flow of the water; first and second outer walls attached at one edge thereof to the first and second middle walls respectively and at the opposite edges to a respective one of the fishway walls, and the first middle and outer walls and the second middle and outer walls each forming an angle therebetween facing towards the flow of the water which is less than 180xc2x0.
Preferably, the outer walls have a top edge which slopes downwardly toward a respective one of the fishway walls.
Advantageously, the middle walls form an acute angle of about 30xc2x0.
Preferably, the angle formed between the respective middle and outer walls is about 75xc2x0.
Advantageously, each weir provides contact with a cross sectional area of water at least 150% that provided by a straight weir between the fishway walls.
Preferably, the center wall is rectangular in shape.
Advantageously, the middle walls are rectangular in shape.
The fishway allows fish to pass upstream around structures such as dams and turbines without extensive reworking of the dam structure or the surrounding area. This design may be adapted for use at many different fish passage locations. The fishway construction of the invention design can be used in new installations or to retrofit existing fishways that have proven ineffective.
Other features and advantages of the invention will be set forth in, or will be apparent from, the detailed description of the preferred embodiments which follows.